This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: For many years, antibiotics have been added to animal feed to help control harmful bacteria and improve growth. But amid concerns about antibiotic resistance—when bacteria adapt to survive treatments that would normally kill them—poultry producers are trying alternatives, including probiotics, which contain helpful bacteria, and essential oils, which come from plants and may have antimicrobial properties.
Researchers at Penn State have now found that feeding broiler chickens an antibiotic, a probiotic or essential oils did not significantly affect the overall diversity of antimicrobial resistance genes. Instead, the chickens' age had a much stronger effect on the resistome—the collection of antimicrobial resistance genes—as the birds grew. The researchers recently reported their findings in Poultry Science.
The findings indicate that the bacterial communities in chickens' guts change as the birds age, rather than in response to a specific feed additive. "Antibiotic resistance is an important problem, and poultry producers are increasingly using products such as probiotics and essential oils instead of antibiotics. However, we don't fully know whether these products affect antibiotic-resistance genes in chickens," said senior study author and team leader Erika Ganda, associate professor of food animal microbiomes in the Penn State College of Agricultural Sciences.
"In this experiment, probiotics and essential oils did not produce substantial or sustained changes in the overall resistome, which supports further investigation of these products as antibiotic alternatives." In the study conducted at the Penn State Poultry Education and Research Center, the researchers fed 320 broiler chickens one of four diets: a normal diet with no additives, a diet containing an antibiotic, a diet containing essential oils and a diet containing a probiotic. They collected fecal samples when the birds were 1, 10 and 21 days old and used DNA sequencing to identify resistance genes. The DNA sequencing method, called shotgun metagenomics, can detect resistance-gene sequences and allow scientists to assess their presence and relative abundance.
But it does not determine whether the bacteria carrying those genes are resistant or whether the genes are actively expressed. In total, the researchers found 823 unique resistance genes. First study author Ana Fonseca, who graduated from Penn State with a dual-title doctorate in animal science and microbiome sciences and is now a poultry management educator with the Penn State Extension Poultry Team, said the research team was somewhat surprised that the antibiotic treatment did not produce a sustained change in the broiler chickens' overall resistome.
She said age was a much stronger factor in shaping the resistance-gene profiles. "The resistome of a 1-day-old chick looked quite different from that of a 10-day-old chick, and the resistome changed again by day 21," she said. "As chickens grow, the community of bacteria living in their gut changes naturally.
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